1. Field of the Invention
The present invention relates to a receiving apparatus that improves reception characteristic deterioration of a radio-frequency signal caused by an interfering wave.
2. Description of Related Art
For a distortion characteristic of a receiver, there are a method of changing automatic gain control (AGC) of a low noise amplifier (LNA) most appropriately (see, for example, JP-A-2005-295471) and a method of improving the characteristic of an MOPLL (Mixer Oscillator Phase Locked Loop).
An MOPLL IC is formed, for example, of a mixer, a voltage-controlled oscillator, and an amplifier, and it down-converts a signal (see, for example, JP-2008-53836). To be more concrete, the mixer extracts an intermediate frequency signal (IF signal) from a radio-frequency signal (RF signal) and a locally-generated signal from the voltage-controlled oscillator, that is, it down-converts an RF signal to an IF signal at a lower frequency.
In general, a mixer is a crucial circuit that has influences on an operation of the overall receiving apparatus. The performance of the mixer is evaluated, for example, by a 3rd-order intermodulation (IM3). The 3rd-order intermodulation referred herein means an interfering signal that overlaps a nearby frequency of or the same frequency as a desired wave when two waves are aligned equally with respect to the desired wave, and it is used as a parameter of distortion. Hence, a resistor element corresponding to a bias resistor is normally provided inside the MOPLL IC. Owing to this configuration, the distortion characteristic is improved.